Estuaries and connected tidal marshes play a critical role in aiding the survival of juvenile salmonid and other aquatic creatures by providing a productive feeding area that is protected from marine predators and a transitional zone for gradual acclimation to salt water. Unfortunately, a tide gate is likely to be installed at the mouth of an estuary to prevent tidal flooding of low lying coastal areas. A tide gate, which prevents the flow of ocean water into the estuary or tidal marsh, destroys the habitat's value to salmonids & other auquatic life by decreasing salinity and dissolved oxygen and increasing the temperature range of the remaining water. In addition, a tide gate disrupts the movement of fish from the ocean into the estuary or other inland water body.
If one were to simply remove the tide gates, however, many structures that had been built since the tide gates' installation would be destroyed. Moreover, agricultural and other developed areas would face a harmful intrusion of salt water. Nevertheless, entry of ocean water into a coastal area could be permitted if the entry was restricted to a level that avoided harm to structures and farms. Unfortunately, heretofore there has been no practical way of accomplishing this goal.